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FBHO & FHRC
 
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boogered chain box shafts

My timing chain tensioner pivot shafts are galled pretty bad in the area that the idler arms ride on. My 3.0 sc had pressure fed tensioners installed but they used a spacer instead of updated, longer idler arms.

The galling was so bad that I could barely removed one of the idler arms. I would like to heat the housings, remove the shafts and replace w/ new shafts.

Does anyone know if these shafts are available as replacement parts?

I will be replacing the idler arms for sure.
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Old 09-03-2004, 06:26 AM
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You may be able to find a set of used boxes that have decent shafts if you cant find new, otherwise just make them.
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Old 09-03-2004, 08:06 AM
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Care to guess what matl to make them out of? 4140, 4130,HSS drill rod?
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Old 09-03-2004, 10:56 AM
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Most likely, anything you make them out of will be stronger than the housing it sits in anyway. Any of the above mentioned steels woudl prob work just fine, the thickness of the shaft and higher tensile strength of those alloys, and possibly even a 17-4 ph, or 9310 if you really want a tough peice, will assist in any side deflection , but again, its rigidity of the mount is more likely to move if at all. Down a simpler route-I would take a look at using a peice of oil hardened drill rod, since the idler pivots on a bronze bushing anyway, you wont have to worry too much about heat treating the surface.
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Old 09-03-2004, 11:55 AM
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Well, I made new shafts out of 15mm O1 ground drill rod purchased from Mcmaster Carr for $10.00 for a 3' length.

I carefully heated the cases then tapped the old shafts out.

Next I measured the old shafts (one is a bit longer than the other). I cut up some new shafts, then machined them to length and turned the one end to the proper diameter.

Next I applied red loctite to the turned down end and CAREFULLY
pressed the new shafts into place (I sized them for a nice light press fit).

Next I slid the chain box covers back on to check that I had indeed pressed the the shafts in squarely. They slid on like a glove.

Now after cleaning I still need to JB Weld the back side of the boxes where the shafts are exposed (per The Book).

If one is careful and has access to a lathe, this procedure is fairly simple and sure beats the price of new chain boxes or questionable condition used boxes.



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Old 09-10-2004, 06:55 AM
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Old 09-10-2004, 08:27 AM
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Very cool! And very enterprising!!


JA
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Old 09-10-2004, 08:59 PM
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I my idler arm bushings look a bit scrubed in the two wear areas. I'm thinking of buffing them up and reinstalling. It seems that there is really no clearance for oil to get in there. What is the dimetral clearance. I'll look on other threads and see if a number is given. I don't see the number in the Wayne book. Thanks,
-Henry
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Old 03-27-2005, 07:58 AM
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Nice! I'm so jealous!
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Old 03-27-2005, 08:02 AM
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Bad idler shafts.

I also bought 3' of ground & polished 15mm rod from McMaster Carr in Chicago. I cut the pieces to length and stuck them in a my drill press at a high rpm and took a file to the area i needed to reduce. After i got the material to .005 from my finished dimension i used a 250- 600 grit sand paper to finish size, all this was done on the drill press. It didnt take me more than 15 minutes per shaft. You need a micromerter, or a very good caliper. Measure shaft in all positions on rod to make sure it is the same dimension all across the lenght of the shaft. Remember the idler arm does not move but a very little bit on these shafts perfect is nice but not absolute.
Old 03-27-2005, 08:18 AM
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Henry: Tne numbers are in the appendix in Waynes book. Look under chain housing. I was looking them up today.
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Old 03-27-2005, 11:13 AM
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OK. I see now thanks. -Henry
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Old 03-27-2005, 11:26 AM
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I'm going to go remeasure. I'm getting almost no diameter difference from bore to shaft. When I put WD-40 on and slide on very carefully I can't feel any radial play sort of like a slip fit. I think this lubrication location is a tough one as the idler doesn't move much just rotates a bit back and forth and there is only the one oil hole in the middle. Also the forces put a constant torque on the two bushings one up and one down.
I also notice that the idler sprocket doesn't seem to be running true with the chain all the wear is on one side....sort of like it is not floating to the middle like it is reported to do per the design.

-Henry
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1989 3.2 coupe, DIY top end at 77k, now 112k
Old 03-27-2005, 11:32 AM
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I made a lapping tool using 400 grit paper and using engine oil was able to take the bore out to the min. of 15.000mm. It sure feels better than before. I sanded the shaft in the cam housing a bit also....I'm still probably not at the min. clearance but better than it was.

A fellow a few miles from here just fired up his 3.2, this morning, after at top end rebuild and everything went fine until 5 minutes of running when the right tensioner failed. I don't want this to happen to me....I'm asking what went wrong and will report.

-h
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Old 03-27-2005, 02:11 PM
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hcoles,

Any word on what happened in the engine of the guy who had the tensioner fail in his newly rebuilt 3.2?

Phil
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Old 04-13-2005, 03:56 PM
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I didn't hear from Jim that he found a root cause. He bought another tensioner installed and finished the 20 minute run in.
I'm doing three things to improve my cam chain arms.
1 - replace bushings with SAE 660 bronze
2 - Jerry Woods spacer inside the tensioner
3 - some amount of shimming to limit the arm movement fore and aft.

IMVHO I think when you slam on the brakes (1-1.5g's) there can be chain movement toward the front of the car until the arm hits the case....this is way to far in my opinion. However I haven't got too many people to bite on this idea. My machinists thinks the shimming is a good idea and I sent in a question to the PCA under Engines...

Considering all the issues people have with oil fed tensioners....surely something is going on that is not identified.... Wayne indicates binding on the arm or maybe inside the tensioners...I think this is on the right track and the pressure feed doesn't protect against this. I think what happens is the arm moves over and "locks" on the arm and then moves back over or not. This matches what I hear people say when they are running on the track......they hear considerable cam chain noise and then after coming in or driving for a bit it goes away. I'm still interested in finding out the complete story on this....we may never know until someone puts a distance sensor near the arm and logs the position fore and aft. As I have said before the next engine designs got ride of the idler wheels and arm.
-H
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Old 04-14-2005, 10:26 AM
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I think all three of your improvements will help. How much space do you have on the shaft between the oil fed tensioner and the arm? I have the updated arms (with bushings) on my car, but there's still about a 3/16th inch gap that would let the arm slide on the shaft. The spacers Pelican sells do not fit (too thick) so I was just curious how much of a shim you're putting on your shaft. I just got finished putting the Jerry Woods spacer inside my oil fed tensioners.

Phil
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Old 04-14-2005, 11:21 AM
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Phil,
I'm not really sure what you mean (space on shaft of tensioner and arm). Maybe I do now that I think of it....when you tighten the nut holding the tensioner it will go to some place on the arm...I don't think a spacer is needed. Very good question. I want to go and look at this again.

Regarding shimming the idler arm so it is a bit more limited....I'm going to put the engine together (at least the cams and cam housing) and then measure how much play is fore and how much play is aft for each arm.

If you are talking about shimming the tensioner it self....I didn't think of that but it is worth thinking about....I didn't find any shims under the tensioner. I'm glad you brought this up as the tip of the tensioner would like to be setup to hit the middle of the pad on the knuckle on the arm.
I'm I making sense?

Sorry for the slow response the kids broke the web connection last night and I just got it going.

-Henry
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Old 04-14-2005, 02:20 PM
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Hi Henry,

Sorry I wasn't clear. I've attached a pic that shows the gap I was talking about. I'm just wondering if there should be any gap here at all. Your posts about shimming things got me to thinking. I think the tensioner body itself does not need any shims since it bolts on tight with a nut to hold it.

Phil

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Old 04-14-2005, 02:53 PM
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Phil,
Yes...I should have figured this out from what you said. I know this and forgot?

You are correct the tensioner itself didn't have shims in stock form. It is interesting to see where the tensioner tip hits the knuckle on the arm. I can't tell from the design where they wanted the arm to press on the tip. I'm guessing all things being equal pressing in the middle would be correct. So maybe some shimming in this area is worthy of discussion.

My understanding is that there is supposed to be space there (your arrow).
As the cam and intermediate shaft move in and out the chain wants to run in a slightly different location. The idler arm slides to get to these locations and therefore needs some space. I don't think the idler needs this much space but I need to find out the end plays for the cam and intermediate shaft and then do some geometry homework plus add a bit and make some shims. I'm not recommending others do this just because I'm looking into it.

Of course when the chain is somewhat in the middle you won't have the full 3/16 on the aft side the space will be split somewhat....I hope.

Thanks for the effort to get the picture.

-Henry
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Old 04-15-2005, 06:24 AM
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